Heat treatment of magnesium base alloys



A. BRANDT March 23, 1943.

HEAT TREATMENT OF MAGNESIUM BASE ALLOYS Original Filed Oct. 8, 1941 Alloy 8 o 1 8 $5 E k a a Q k XS Patented Mar. 23, 1943 HEAT TREATMENT OF MAGNESIUM BASE ALLOYS Alfred Brandt, Swansea, Wales, assignor, by mesne assignments, to The Anglo California National Bank of San Francisco, San Francisco, Calif., a national banking association, as trustee Original application October 8, 1941, Serial No. 414,176. Divided and this application March 13, 1942, Serial N0.,434,599.

September 9, 1940 6 Claims.

This invention relates to cast magnesium base alloys which contain not less than about 80% of magnesium, and is particularly concerned with raising the yield point (proof stress) of the alloys by subjecting the same in the as-cast condition to a single-step heat treatment within a range of not less than 100 C. but less than 250 0., having avoided any previous thermal treatment at higher temperatures.

It is an object of the present invention to avoid the so-called solution heat treatment at temperatures far above 250 which constitutes,

with subsequent chilling, the first stage of the thermal treatment of magnesium base alloys which has theretofore been the standard practice in treating castings of this type, an annealing treatment at a lower temperature, below 200 C., being preferably carried out as a second stage; The single-step thermal treatment at low temperatures leaves the strength of the material substantially unaltered, and the elongation may even decrease to some extent. n the other hand, the yield point is materially increased. Uniformity of results, reduction of wastage, the lessening of fire risks, are also possible advantages.

According to the present invention, the singlestep heat treatment between 100 C. and 250 C. is applied to magnesium base alloys of the aluminum-tin-silver system, containing not less than about 80% of magnesium and containing the alloying constituents in a total amount of 1% to 12%. Alloys of this system particularly susceptible to improvement by such single-stepheat treatment at low temperature are such containing from about 2% to about 6% of aluminum, and also containing from about 0.10% to about 4% of silver and from'about 2.75% to about 10% of tin, the total amount of the alloying additions being not above 12%, which alloys generally are described in D. T. D. Specification No. 350 of the British Air Ministry Department of Technical Development (see page 229 of Metal Industry Handbook, 1924 ed.)

The following examples give the percentages by weight of the castings (subject to tolerance for usual impurities) according to preferred embodiments of the invention:

In Great Britain The drawing illustrates the eifect of heat treatment of the cast alloys of the examples, the top line of the columns indicating the yield point (taken in tons per square inch) for 0.1% permanent deformation of the heat-treated casting, the line in the same column somewhat below it indicating the yield point of the unheat-treated alloy, that is, in the as-cast condition. The alloy indicated by (1) was treated for three days at C. and the alloy indicated by (2) was treated for three days at C.

This application is a division of my application Serial No. 414,176, filed October 8, 1941.

I claim:

1. A method for improving the yield point of cast magnesium base alloys consisting of aluminum from about 2.0% to about 6.0%, tin fromabout 2.75% to about 10.0%, silver from about 0.1% toabout 4.0%, the balance substantially all magnesium, the total amount of said alloying constituents being not above 12%, which comprises subjecting such alloys in the as-cast condition to a heat treatment at a temperature within the range 100 C. to 250 C.

2. A method for improving the yield point of a cast magnesium base alloy consisting of, aluminum about 3.75%, tin about 5.68%, silver about 1.2%, the balance substantially all magnesium,

which comprises subjecting such allow in the ascast condition to a heat treatment at a temperature within the range 100 C. to 250 C.

3. A method for improving the yield point of a cast magnesium base alloy consisting of, aluminum about 1.91%, tin about 2.78%, silver about 0.14%, the balance substantially all magnesium, which comprises subjecting such alloy in the ascast condition to a heat treatment at a temperature within the range 100 C. to 250 C.

4. An alloy consisting principally of magnesium and containing aluminum from about 2.0% to about 6.0%, tin from about 2.75%to about 10.0%,

and silver from about 0.1% to about 4.0%, the I balance substantially all magnesium, the total amount of said alloying constituents not exceeding 12% in the form of shaped castings the yield point of which has been raised without appreciable increase in strength by a heat treatment in the as-cast condition at a temperature within the range of 100 C. to 250 C.

5. An alloy consisting principally of magnesium and containing aluminum about 3.75%, tin about 5.68%, silver about 1.2%, the balance substantially all magnesium'in the form of a shaped casting the yield point of which has been raised without appreciable increase in strength by a heat treatment in the "as-cast condition at a temperature within the range of 100- C. to 250 C.

6. An alloy consisting principally of magnesium and containing aluminum about 1.91%, tin about 2.78%, silver about 0.14%, the balance subtemperature within the range of 100 C. tov

ALFRED BRANDT. 

